Active matrix substrate for liquid-crystal display and method of fabricating the active matrix substrate

ABSTRACT

In an active matrix substrate for a liquid-crystal display, a plurality of individual transparent electrodes are arranged in the form of an array, and an array of thin-film transistors is connected to the transparent electrodes for driving the same. Each of the thin-film transistors includes a source region and a drain region which are formed such that impurities are doped at high concentration, an active layer composed of a silicon thin film which is in contact with the source and drain regions and in which at least a part of the silicon thin film covers the source and drain regions, an insulating film which covers the source and drain regions and the active layer, and a gate electrode on the insulating film. Each of the individual transparent electrodes is composed of a silicon thin film contiguous to the active layer of the thin-film transistor and a metal silicide on the silicon thin film. In the active matrix substrate, metal silicide is formed, in the form of an island, onto the silicon thin film on the entire surface of which the individual transparent electrodes are formed. The active matrix substrate of the invention does not use a transparent conductive film made of indium as indium tin oxide and oxide of tin. A pair of drain regions may be so formed as to electrically shield the source region. A method of fabricating the active matrix substrate is also disclosed.

This application is a division, of prior application Ser. No.07/570,382, filed Aug. 21, 1990 now U.S. Pat. No. 5,191,453.

BACKGROUND OF THE INVENTION

The present invention relates to an active matrix substrate for aliquid-crystal display, which has a thin-film transistor serving as anactive element, and a method of fabricating the active matrix substrate.

In recent years, development in an active-matrix type liquid-crystaldisplay has been remarkable with the object being to make a display flator plane. The active matrix type is such that a thin-film transistor ora thin-film diode of an active element is incorporated as a switchingelement in each picture element or pixel. The active matrix type is socharacterized as to obtain high picture quality, as compared with aso-called simple matrix type in which transparent electrodes are simplyintersected with each other.

As a conventional example, an active matrix substrate will be describedhere in which a thin-film transistor of poly-crystalline silicon isused. FIGS. 6(a) and 6(b) show the conventional example which isdisclosed in "SID '88 Digest", H. Ohshima et al., Lecture No. 21.4, pp408-411. FIG. 6(a) is a top plan view showing one of a plurality ofpicture elements, while FIG. 6(b) is an enlarged cross-sectional viewtaken along the line VI(b)-VI(b) in FIG. 6(a).

The conventional active matrix substrate comprises a glass substrate 1and a pair of source and drain regions 3 and 2 on the glass substrate 1.The source and drain regions 3 and 2 are composed of poly-crystallinesilicon in which phosphorus is doped at high concentration. An activelayer 4 composed of an undoped poly-crystalline silicon thin film isprovided on the source and drain regions 3 and 2 in contact therewith.The active layer 4 is covered with a gate insulating film 5 made ofsilicon dioxide. On the gate insulating film 5 there is provided a gateelectrode and gate line 6 made of chromium. The gate electrode 6 iscovered with an interlayer insulating film 7 made of silicon dioxide.The interlayer insulating film 7 is partly covered with apicture-element electrode 8 which is composed of a transparentconductive element made of indium tin oxide. A drain signal line 9 isprovided which is made of aluminum.

An example of a method of fabricating the active matrix substrate isillustrated in FIGS. 7(a) through 7(d) and will next be described in dueorder.

(1) A poly-crystalline silicon containing a high concentration ofphosphorus is formed on a glass substrate by a low-pressure CVD(chemical vapor deposition) process which uses phosphine (PH₃) andsilane (SiH₄) as raw-material gas. The poly-crystalline silicon ispatterned to form the source region 3 and the drain region 2.Subsequently, silane is decomposed similarly by the low-pressure CVDprocess to form a poly-crystalline silicon thin film on the source anddrain regions 3 and 2. The poly-crystalline silicon thin film ispatterned in the form of an island to form the active layer 4.

(2) The gate insulating film 5 consisting of a silicon dioxide film isformed on the active layer 4 by a CVD process which uses silane andoxygen as raw-material gas. Chromium is formed on the gate insulatingfilm 5 by means of sputtering and is subsequently patterned to form thegate electrode 6.

(3) The interlayer insulating film 7 consisting of silicon dioxide isformed on the gate electrode 6 again by means of the CVD process. A pairof contact holes to the respective source and drain regions 3 and 2 areformed in the silicon dioxide films 5 and 7.

(4) Lastly, the drain line 9 made of aluminum and the picture-elementelectrode 8 made of indium tin oxide are formed into their respectivefilms by means of a sputtering process or a vacuum deposition processand, subsequently, are patterned into their respective desiredconfigurations. Thus, the fabricating method is completed.

The above-described construction and fabricating method have variousproblems caused by the use of the indium tin oxide. First, inferiorityin etching of the indium tin oxide can be given. That is, the indium tinoxide has the following problems. Although superior in nature as atransparent conductive film, the indium tin oxide involves difficultiesin dry etching, is not so good in processing accuracy at wet etching,and so on. For this reason, it is necessary to take a sufficient spacemore than 5 μm between the line and the individual transparent electrodemade of indium tin oxide. This space becomes one of causes which reducethe area of the transmitting section of a light. Secondly, there is sucha problem that etchant for the wet etching etches also aluminum.Accordingly, in the case where the indium tin oxide and the aluminumline are on the same or identical plane as in this example, a very highetching technique is required. Thirdly, there is such a problem that theindium tin oxide is apt to be damaged by hydrogen plasma. Although it isnecessary to decrease the trap density in grain boundary as a necessitypeculiar to the poly-crystalline silicon, the hydrogen plasma treatmentis a technique which is often used. In this construction, however, sincethe indium tin oxide forms the uppermost layer, it is difficult toimprove the transistor characteristic by use of the hydrogen plasmatreatment at the last step. As another problem, the involvement of anumber of the fabricating steps can be given. In this example, six (6)masks are used. The large number of the steps causes reduction of theyield.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an active matrix substratefor a liquid-crystal display, which solves the above-discusseddisadvantages of the prior art, which has no problem caused by indiumtin oxide, which is simple in construction and which is less infabricating steps.

It is another object of the invention to provide a method of fabricatingthe above-described active matrix substrate.

According to the invention, there is provided an active matrix substratefor a liquid-crystal display comprising:

a substrate;

a plurality of pixel electrodes formed on the substrate in a matrixform, each of the pixel electrodes having a first silicon thin film anda metal silicide film formed on the first silicon thin film; and

a plurality of thin-film transistors formed on the substrate andconnected to the pixel electrodes, respectively, each of the thin-filmtransistors having a second silicon thin film continuous with the firstsilicon thin film, a gate electrode formed on one of an upper surfaceand a lower surface of a portion of the second thin film, and a sourceand drain regions formed at both sides of the gate electrode, the sourceand drain regions being connected to the portion of the second thinfilm, and one of the source and drain regions being electricallyconnected to the pixel electrode.

According to the invention, there is further provided an active matrixsubstrate for a liquid-crystal display comprising a plurality ofindividual transparent electrodes arranged in the form of an array, andan array of thin-film transistors connected to the transparentelectrodes for driving the same, each of the thin-film transistorsincluding:

a source region and a drain region which are formed such that impuritiesare doped at high concentration;

an active layer composed of a silicon thin film which is in contact withthe source and drain regions and in which at least a part of the siliconthin film covers the source and drain regions;

an insulating film which covers the source and drain regions and theactive layer; and

a gate electrode on the insulating film,

wherein each of the individual transparent electrodes is composed of asilicon thin film contiguous to the active layer of the thin-filmtransistor and a metal silicide on the silicon thin film.

According to the invention, there is still further provided an activematrix substrate for a liquid-crystal display, the active matrixsubstrate comprising a plurality of individual transparent electrodesarranged in the form of an array, and an array of thin-film transistorsconnected to the transparent electrodes for driving the same, each ofthe thin-film transistors including:

a source region formed such that impurities are doped at highconcentration;

a drain region formed in such a configuration as to electrically shieldthe source region;

an active layer composed of a silicon thin film which is in contact withthe source and drain regions and in which at least a part of the siliconthin film covers the source and drain regions;

an insulating film which covers the source and drain regions and theactive layer; and

a gate electrode on the insulating film,

wherein each of the individual transparent electrodes is composed of asilicon thin film formed on the entire surface of the substrate and ametallic silicide on the silicon thin film formed in the form of anarray.

According to the invention, there is still further provided a method offabricating an active matrix substrate for a liquid-crystal display, themethod comprising the steps of:

forming a first silicon film in which impurities high in concentrationare doped onto a transparent substrate, and patterning the first siliconthin film into source and drain regions and configurations of connectionportions at intersected sections of lines;

forming a second silicon thin film on the source and drain regions andthe connection portions, and patterning the second silicon thin filminto island regions in contact with at least the source and drainregions and an island region contiguous to the island regions, which isslightly larger than the configuration of an individual transparentelectrode;

forming an insulating film on the second silicon thin film;

forming a pair of holes in the insulating film, for being in contactwith the source and drain regions, and a hole identical with theconfiguration of the individual transparent electrode, on the secondsilicon thin film which is patterned into the island region slightlylarger than the individual transparent electrode;

forming metal on the second silicon thin film, the metal reacting atleast with silicon to form silicide;

heat-treating the metal to form the silicide; and

patterning the metal to form lines for a gate, and the source and drainregions.

According to the invention, there is also provided a method offabricating an active matrix substrate for a liquid-crystal display, themethod comprising the steps of:

forming a first silicon thin film in which impurities high inconcentration are doped onto a transparent substrate, and patterning thefirst silicon thin film into source and drain regions and configurationsof connection portions at intersected sections of lines;

forming a second silicon thin film on the source and drain regions andthe connection portions;

forming an insulating film on the second silicon thin film;

forming a pair of holes in the insulating film, for being in contactwith the source and drain regions, and a hole identical with theconfiguration of an individual transparent electrode;

forming metal on the second silicon thin film, the metal reacting atleast with silicon to form silicide;

heat-treating the metal to form the silicide; and

patterning the metal to form lines for a gate, and the source and drainregions.

The active matrix substrate for the liquid-crystal display according tothe invention forms the individual transparent electrode by the siliconthin film and the metal silicide thereon without the use of indium tinoxide. The processing accuracy of the silicon thin film is higher by onefigure than the indium tin oxide, and it is unnecessary to take muchmargin between the line and the individual transparent electrode. As aresult, it is possible to increase the aperture ratio more than theconventional one. Further, there is no problem in selection of etchingwith respect to aluminum, and there is no problem of damage caused bythe hydrogen plasma treatment.

Furthermore, since the silicon thin film of the individual transparentelectrode and the active layer of the driving thin-film transistor areformed in contiguous to each other, the construction is made simple. Forthis reason, it is possible to form together the active layer of thethin-film transistor and the individual transparent electrode section.Thus, it is possible to reduce the fabricating steps.

Moreover, the active layer of the thin-film transistor and the siliconthin film of the individual transparent electrode section may be formedon the entire surface of the substrate without being patterned. In thiscase, if the source region is so formed as to be electrically shieldedby the drain region, it is possible to block leak current from the drainline for other picture elements or pixels. Since, in such construction,the patterning step of the silicon thin film can be dispensed with,there is obtained such an advantage that the fabricating steps canfurther be simplified.

In the case where the silicon thin film containing silicide is used asthe transparent electrode, light transmittance becomes a problem. Thetransmittance relies upon the film thickness. In the case of thepoly-crystalline silicon film, the film thickness in the order of 300 Åindicates 75% or more of the light transmittance. Thus, the thin filmcan sufficiently withstand practical use. As an example, therelationship between the transmittance and the film thickness of thepoly-crystalline silicon film was measured on lights whose respectivewavelengths are 460 nm, 540 nm and 660 nm. The measurement results areshown in FIG. 8. Since a single-crystalline silicon film is higher intransmittance than the poly-crystalline silicon film, it is possible touse the thickness in the order of 1,000 Å. Further, since an amorphoussilicon film is low in transmittance, it is desirable to use theamorphous silicon film with its film thickness of the order of 100 Å to200 Å.

In order to increase the transmittance beyond 60% at the wavelength of400 nm-700 nm, it is required for the film thickness to be:

Less than 1000 Å in single-crystalline silicon film,

Less than 400 Å in poly-crystalline silicon film, and

Less than 200 Å in amorphous silicon film.

Therefore, the thickness of the film at its silicon film formation andthe thickness of the film after its silicide formation (50 Å inthickness) may be as follows:

    ______________________________________                                                  Silicon film                                                                           After silicide formation                                   ______________________________________                                        Single-crystalline                                                                         150-1050 Å                                                                           100-1000 Å                                        Poly-crystalline                                                                          150-450 Å                                                                            100-400 Å                                          Amorphous   150-250 Å                                                                            100-100 Å                                          ______________________________________                                    

Here, since the silicide film is extremely thin, e.g. 20-50 Å, thesilicide film absorbs light very little, and the light is transmittedthrough the silicide film. Thus, there is no problem. Furthermore,although the silicon thin film is extremely large in resistance, the useof the silicide film enables the sheet resistance to be reducedrelatively to a few kΩ. This value is sufficient for the transparentelectrodes for picture elements (pixels).

As will be seen from the above-described construction, the active matrixsubstrate for the liquid-crystal display, according to the invention,does not use a transparent conductive film made of indium such as indiumtin oxide and oxide of tin. Accordingly, no problem caused by thetransparent conductive film occurs, unlike in the conventionalsubstrate. In the invention, a window is formed in the silicon dioxidefilm to form the silicide in the polycrystalline silicon film. As knownwell at present, the silicon and the silicon dioxide are high inprocessing accuracy, and it is possible to dry-etch the silicon and thesilicon dioxide at the order of submicron. There is not any problem inapplication of the kind referred to above. The processing accuracy ofthe silicon and the silicon dioxide is accurate by more than one figurewith respect to the processing accuracy of the indium tin oxide.Further, since the silicon and the silicon dioxide are wholly differentin etchant from aluminum, there occurs no problem in the use of thealuminum, the etching condition and so on. Furthermore, deteriorationcaused by the hydrogen plasma does not appear at all in the silicon andthe silicon dioxide.

The next important factor is the number of steps. Conventionally, six(6) or seven (7) masks are required to be used. However, the number ofthe masks is reduced to three (3) or four (4) in the invention. Thus,the number of steps is reduced approximately to half. The reduction inthe number of steps improves the yield, and is useful in sharp reductionof the manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be apparent from the following description of preferredembodiments of the invention explained with reference to theaccompanying drawings, in which:

FIG. 1(a) is an enlarged fragmentary top plan view of an active matrixsubstrate for a liquid-crystal display, according to a first embodimentof the invention;

FIG. 1(b) is a cross-sectional view taken along the line I(b)--I(b) inFIG. 1(a);

FIGS. 2(a) through 2(e) are views showing a fabrication method accordingto the first embodiment of the invention;

FIG. 3(a) is an enlarged fragmentary top plan view of an active matrixsubstrate for a liquid-crystal display, according to a second embodimentof the invention;

FIG. 3(b) is a cross-sectional view taken along the line III(b)--III(b)in FIG. 3(a);

FIG. 3(c) is a cross-sectional view taken along the line III(c)--III(c)in FIG. 3(a);

FIGS. 4(a) through 4(e) are views showing a fabrication method accordingto the second embodiment of the invention;

FIG. 5(a) is an enlarged fragmentary top plan view of an active matrixsubstrate for a liquid-crystal display, according to a third embodimentof the invention;

FIG. 5(b) is a cross-sectional view taken along the line V(b)--V(b) inFIG. 5(a);

FIG. 6(a) is an enlarged fragmentary top plan view of the conventionalactive matrix substrate for a liquid-crystal display;

FIG. 6(b) is a cross-sectional view taken along the line VI(b)--VI(b) inFIG. 6(a);

FIGS. 7(a) through 7(d) are views showing the conventional method offabricating the active matrix substrate illustrated in FIGS. 6(a) and6(b); and

FIG. 8 is a graphical representation showing the relationship betweenthe film thickness of a silicon thin film and the transmittance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIRST EMBODIMENT

Referring first to FIGS. 1(a) and 1(b), there is shown, in top plan andcross-sectional views, an active matrix substrate for a liquid-crystaldisplay, according to a first embodiment of the invention. The activematrix substrate comprises a pair of source and drain regions 101 and102 each of which is made of a poly-crystalline silicon film in whichphosphorus is doped at high concentration. The source and drain regions101 and 102 are covered with an active layer 103 which is made of apoly-crystalline silicon film and whose thickness is, for example, 300Å. As to the film thickness of the active layer 103 in a thin-filmtransistor, it is required that the film be within the minimum of 50-100Å. The active layer 103 is covered with a gate insulating film 104 whichis made of a silicon dioxide film. The gate insulating film 104 iscovered with a gate electrode and gate line 105, a drain electrode anddrain line 106, and a source electrode 107, which are all made ofchromium. The active matrix substrate further comprises a chromiumsilicide film 108 which cooperates with the poly-crystalline siliconfilm (the active layer 103) to form an individual transparent electrode.The metal silicide film is formed of a member selected from a groupconsisting of chromium silicide, molybdenum silicide, nickel silicideand platinum silicide and compounds thereof. The preferable filmthickness of such metal silicide film is within 20-100 Å with 20 Å beingthe lower limit for the formation of silicide. Above 100 Å, it becomesdifficult to obtain sufficient transmittance for transparent electrodes.Indium tin oxide is not used at all in the active matrix substrateaccording to the invention.

A method of fabricating the active matrix substrate for theliquid-crystal display, according to the first embodiment of theinvention, will next be described with reference to FIGS. 2(a) through2(e).

(A) A poly-crystalline silicon containing a high concentration ofphosphorus is formed on a glass substrate by a low-pressure CVD(chemical vapor deposition) process which uses phosphine (PH₃) andsilane (SiH₄) as raw-material gas. The poly-crystalline silicon ispatterned to form the source region 101 and the drain region 102.Subsequently, silane is decomposed similarly by the low-pressure CVDprocess to form a poly-crystalline silicon thin film on the source anddrain regions 101 and 102, to form the active layer 103. The activelayer 103 is then patterned.

(B) The active layer 103 is covered with the gate insulating film 104consisting of a silicon dioxide film by a CVD process which uses silaneand oxygen as raw-material gas.

(C) A pair of contact holes are formed in the silicon dioxide film 104,and chromium 205 is formed by a sputtering process.

(D) The chromium 205 is heat-treated at 200° C. to 300° C. Thus, thechromium silicide layer 108 is formed.

(E) The chromium 205 is patterned into a desirable configuration. Thus,the active matrix substrate is completed.

As will be seen from the foregoing, patterning steps using photomasksare a total of four (4) including the first n-type poly-crystallinesilicon, the poly-crystalline silicon of 300 Å, the contact holes to thesilicon dioxide, and the patterning of chromium.

Second Embodiment

Referring next to FIGS. 3(a) through 3(c), there is shown, in top planand cross-sectional views, an active matrix substrate for aliquid-crystal display, according to a second embodiment of theinvention. The active matrix substrate of this embodiment comprises ashield drain region 301, a source region 302 and a drain region 303 eachof which is made of a poly-crystalline silicon film in which phosphorusis doped at high concentration. The shield drain, source and drainregions 301, 302 and 303 are covered with an active layer 304 which ismade of a poly-crystalline silicon film and whose thickness is 300 Å.The active layer 304 is covered with a gate insulating film 305 which ismade of a silicon dioxide film. The gate insulating film 305 is coveredwith a gate electrode and gate line 306 made of chromium. A sourceelectrode 307 is similarly made of chromium. Numeral 308 represents achromium silicide film. A drain line 309 is also made of chromium. Inthis construction, the chromium silicide film 308 cooperates with thepoly-crystalline silicon film (the active layer 304) of 300 Å to form anindividual transparent electrode. Indium tin oxide is not used at all inthe active matrix substrate.

In the construction mentioned above, the source region 302 is surroundedby the shield drain region 301 and the drain region 303, and iselectrically shielded from other drain regions. Further, the largeststeps or level differences in the structure are those which are formedby the respective sections of the shield drain region 301, the sourceregion 302 and the drain region 303, and each of which is of the orderof 0.1 μm to 0.15 μm. As a point different from the conventionalexample, it can be said that the poly-crystalline silicon film (theactive layer) 304 is not patterned at all. Even if the poly-crystallinesilicon film 304 is not patterned, however, there is no problem incharacteristic, because the poly-crystalline silicon film is extremelythin. This is because, since the film is extremely thin, electronsserving as carrier can easily pass through it vertically, whileelectrons are extremely difficult to pass laterally. Particularly, atthe section of the contacts, there are diffusion of impurities from then-type poly-crystalline silicon constituting a foundation at formationof the poly-crystalline film, and reduction in film thickness atformation of the chromium silicide. Thus, even without any gravings,there is obtained an excellent ohmic contact.

A method of fabricating the active matrix substrate for theliquid-crystal display, according to the second embodiment of theinvention, will next be described with reference to FIGS. 4(a) through4(e).

(A) A poly-crystalline silicon containing a high concentration ofphosphorus is formed on a glass substrate by a low-pressure CVD processwhich uses phosphine (PH₃) and silane (SiH₄) as raw-material gas. Thepoly-crystalline silicon is patterned to form the source and drainregions 301 and 302.

(B) Subsequently, silane is decomposed similarly by the low-pressure CVDprocess to form a poly-crystalline silicon thin film on the source anddrain regions 302 and 301, to form the active layer 304. The activelayer 304 is covered with the gate insulating film 305 consisting of asilicon dioxide film by a CVD process which uses silane and oxygen asraw-material gas.

(C) A pair of contact holes are formed in the silicon dioxide film 305,and the chromium 306 is formed on the silicon dioxide film 305 by asputtering process.

(D) The chromium 306 is heat-treated at 200° C. to 300° C. Thus, thechromium silicide layer 308 is formed.

(E) The chromium 306 is patterned into a desirable configuration. Thus,the active matrix substrate is completed.

As will be seen from the foregoing, patterning steps using photomasksare a total of three (3) including the first n-type poly-crystallinesilicon, the contact holes to the silicon dioxide, and the patterning ofchromium.

Third Embodiment

Referring next to FIGS. 5(a) and 5(b), there is shown, in top plan andcross-sectional views, an active matrix substrate for a liquid-crystaldisplay, according to a third embodiment of the invention. FIG. 5(b) isa cross-sectional view taken along the line V(b)--V(b) in FIG. 5(a). Theactive matrix substrate comprises a source region 401 and a drain region402 each of which is made of an n-type poly-crystalline silicon film.The source and drain regions 401 and 402 are covered with an activelayer 403 which is made of a poly-crystalline silicon film and whosethickness is 300 Å. The active layer 403 is covered with double-layeredgate insulating films 404 and 405 which are made respectively of asilicon dioxide film and a silicon nitride film. The gate insulatingfilms 404 and 405 are covered with double-layered gate electrodes 406and 407 which are made respectively of chromium and aluminum. Numeral408 represents a chromium silicide film. A drain line 409 has itsconstruction the same as that of the gate electrode.

Even if the active matrix substrate is arranged as in this embodiment,it is possible to shield leak current from the drain lines for otherpicture elements. Further, in this embodiment, each of the gateinsulating films and the gate electrodes is formed by the double-layeredfilms. The reason as to why the gate insulating films of double-layerconstruction is used is as follows. That is, the interface between thegate insulating film and the poly-crystalline silicon is formed bysilicon dioxide which is low in trap-density. On the other hand, asilicon nitride film relatively large in dielectric constant is used onthe silicon dioxide film, whereby the total thickness is increased so asto withstand short-circuiting defects caused such as by pin holes. Sincethe silicon nitride is formed within plasma including hydrogen, thehydrogen plasma treatment is practiced automatically. The reason as towhy the gate electrode of double-layer construction is used is asfollows. That is, the use of the aluminum at the upper section has suchan advantage as to reduce the line resistance. These are likewiseapplicable also to the aforementioned first embodiment. In this manner,even if the double-layer films are used, the number of the masks isthree (3).

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

What is claimed is:
 1. A method of fabricating an active matrixsubstrate for a liquid-crystal display having a plurality of individualtransparent electrodes and a plurality of thin-film transistors botharranged in a matrix form, said method comprising the steps of:forming afirst silicon thin film in which impurities high in concentration aredoped onto a transparent substrate, and patterning said first siliconthin film into source and drain regions; forming a second silicon thinfilm on said source and drain regions, and patterning said secondsilicon thin film into a first island region which covers said sourceand drain regions and a second island region which is contiguous to saidfirst island region and is slightly larger than the configuration ofsaid transparent electrode; forming an insulating film on said secondsilicon thin film; forming in said insulating film at least a pair ofcontact holes over said source and drain regions, and a hole identicalwith the configuration of said individual transparent electrode on saidsecond island region of said second silicon thin film; forming a metalsilicide by heat-treating said metal; and patterning said metal to forma gate, a source, and a drain line.
 2. A method of fabricating an activematrix substrate for a liquid-crystal display having a plurality ofindividual transparent electrodes and a plurality of thin-filmtransistors both arranged in a matrix form, said method comprising thesteps of:forming a first silicon thin film in which high concentrationsof impurities are doped onto a transparent substrate, and patterningsaid first silicon thin film into source and drain regions; forming asecond silicon thin film on said source and drain regions; forming aninsulating film on said second silicon thin film; forming in saidinsulating film at least a pair of contact holes over said source anddrain regions, and a hole identical with the configuration of saidtransparent electrode; forming metal on said second silicon thin film,said metal reacting with at least silicon in order to form silicide;forming a metal silicide by heat-treating said metal; and patterningsaid metal to form a gate, a source and a drain line.